Confidential manuscript submitted to Geophysical Research Letters
Supporting Information for “Integrating GPS with GLONASS for high-rate seismogeodesy” Jianghui Geng1 , Peng Jiang1 , Jingnan Liu1 1 GNSS
Research Center, Wuhan University, Wuhan, Hubei, China.
Contents 1. Text S1 2. Figures S1 to S9 3. Table S1
Introduction This supplementary contains a detailed description (Text S1) on the high-rate GPS and GLONASS data processing and subsequent time series analysis. The raw observations can be found from the internet addresses shown in Table S1. Nine more figures (Figures S1–S9) are presented here to enhance and augment the results and discussion in the main text.
Text S1. Details on GPS and GLONASS data analysis We used PPP to process 31 days (day 122–152 of 2016) of 1-Hz GPS and GLONASS data collected at 99 stations in Europe and also those from two earthquakes, i.e., the May 12th Nepal Mw7.3 event and the September 16th Illapel Mw8.3 event (Figure S1). Daily observations with more than 5% of epochs missing (1.2 hours) were excluded. Satellite orbits and Earth rotation parameters were provided by ESOC (European Space Operations Centre) and we fixed them to estimate 1-Hz satellite clock corrections with another group of stations located in the surrounding areas (red solid circles in the inset of Figure S1). A 10◦ cut-off angle for usable observations and elevation dependent weighting for satellites below 30◦ were applied. Carrier-phase and pseudorange measurements of both GPS and GLONASS were weighted with a precision of 0.006 cycles and 3.0 m, respectively. We corrected for antenna phase center offset and variations, phase wind-up effects, attitudes of eclipsing satellites as well as tidal displacements where ocean tides were calculated with FES2004. Firstorder ionosphere delays were eliminated with dual-frequency data while zenith troposphere delays were estimated as random walk parameters based on the global pressure/temperature model and projected onto slant directions with the global mapping function. Positions were estimated at each epoch without any temporal constraints. We enabled ambiguity fixing for both GPS and GLONASS after applying differential code biases and code-phase biases. One-Hz displacements of each station were calculated against its daily position estimates. A cluster analysis based on the BIRCH (Balanced Iterative Reducing and Clustering using Hierarchies) and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithms was then carried out to compress the displacements and afterwards screen out outliers. Note that the “compression” here means that the original displacements were divided into several clusters according to their spatial distances in order to facilitate subsequent outlier rejections. We accomplished sidereal filtering for each 24-hour GPS-only solution by first shifting its epochs forward by 246 s, and then deducting multipath corrections produced by low pass filtering (a fourth-order Chebyshev Type II filter) the preceding 24 hours of data with a cut-off frequency of 10 s.
Corresponding author: Jianghui Geng,
[email protected]
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Confidential manuscript submitted to Geophysical Research Letters
In succeeding spectral analysis, since only displacements instead of absolute positions are appreciated in GNSS seismology, we first removed the mean from each displacement time series, and then filled in data gaps with linear interpolations. Multi-taper power spectra analysis was performed for each 24-hour time series using the discrete prolate spheroidal sequences. For each station on each day, we normalized the power spectral densities (PSDs) for all its five solutions above against the largest PSD derived from the GPS-only float solution. We then, specific to each frequency component, averaged all PSDs (around 2200) for each type of solution, and finally converted the resultant mean PSDs into decibel units with respect to 1 cm2 /Hz.
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Confidential manuscript submitted to Geophysical Research Letters
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a) Distribution of 99 stations (all symbols in the major panel) used for GPS and GLONASS
PPP, as well as 35 stations used for satellite clock estimations (red solid circles in the inset) in Europe. Seven baselines whose lengths are shorter than 2 km are denoted as red open triangles with site codes aside. Black crosses denote the 14 stations spanning an area of about 500×500 km in Spain. The red solid star represents station FFMJ which is located approximately in the middle of the network. b) Distribution of stations used for the May 12th Nepal Mw7.3 event and the epicenter location. c) Distribution of stations used for the September 16th Illapel Mw8.3 event and the epicenter location.
Table S1. Internet addresses for GNSS data and satellite products in this study.
CDDIS CMONOC CODE ESA EUREF IPOC RAMSAC RGP
ftp://ftp.cddis.eosdis.nasa.gov http://www.cmonoc.cn ftp://ftp.unibe.ch/aiub ftp://dgn6.esoc.esa.int/products ftp://igs.bkg.bund.de http://www.ipoc-network.org http://www.ign.gob.ar http://rgp.ign.fr
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Confidential manuscript submitted to Geophysical Research Letters
Displacements in the east component relative to pre−event ground truth (cm)
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Seconds of day 259 for the 2015 Illapel Mw8.3 event Figure S2.
One-Hz displacements (cm) in the east component at four stations for two major earthquakes
in 2015 (i.e., the May 12th Nepal Mw7.3 and the September 16th Illapel Mw8.3 events). The static displacements derived from daily solutions are 1.3, 26.1, 0.5 and 0.6 cm for stations TIBT, TOLO, RCSD and MRCG, respectively. More descriptions refer to Figure 1 in the main text. Note that TOLO experienced pronounced early post-seismic motions to the west on day 260, which explains the over 2 cm bias between the static offsets estimated from the high-rate and daily solutions.
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Displacements in the up component relative to pre−event ground truth (cm)
Confidential manuscript submitted to Geophysical Research Letters
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Seconds of day 259 for the 2015 Illapel Mw8.3 event Figure S3.
One-Hz displacements (cm) in the up component at four stations for two major earthquakes in
2015 (i.e., the May 12th Nepal Mw7.3 and the September 16th Illapel Mw8.3 events). The static displacements derived from daily solutions are −0.9, 2.0, 1.4 and −0.3 cm for stations TIBT, TOLO, RCSD and MRCG, respectively. More descriptions refer to Figure 1 in the main text.
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Confidential manuscript submitted to Geophysical Research Letters
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Seconds of day 259 for the 2015 Illapel Mw8.3 earthquake Figure S4.
One-Hz displacements (cm) at station ZAPA during the September 16th 2015 Illapel Mw8.3
event. Seismic waves arrived at around 82600 s. Introducing GLONASS improves the reliability of high-rate GNSS positioning for all three components and manifests the static displacement in the east component.
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Confidential manuscript submitted to Geophysical Research Letters
GPS fixed GPS fixed sidereal (246s) GPS fixed sidereal (246±20s) 0.0001
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Averaged PSD (dB) over all 80 available stations (Figure S1) on day 123 for the north, east and
up components spanning a wide frequency band from 2 to 50000 s. The black curves denote GPS-only fixed solutions and the blue curves denote sidereally filtered GPS-only fixed solutions wtih a fixed 246 s shift. The green curves also denote sidereally filtered GPS-only fixed solutions, but the shift periods within 226–266 s were all tried to produce 41 sidereally filtered solutions for each station. We then identify the smallest PSD for each frequency component from the spectra of the 41 solutions to plot the green curves. It can be seen that tuning the 246 s shift has discernible impact on the periods of 10–100 s, but little on the low-frequency bands (>1.4 hours). N
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Figure S6.
Sky plot of GPS and GLONASS satellite tracks observed at station FFMJ on day 122 of 2016 in
Europe (Figure S1). The red tracks are for GPS whereas the blue tracks for GLONASS. A 10◦ cut-off angle is applied. The concentric circles in black represent different elevations and the center is the zenith. The most outer circle is for the horizon and graduated with azimuth. The “hole” area in the northern sky is because GNSS satellites do not trace near polar orbits, but with an inclination relative to the Earth’s equator. This hole area can be diminished after the addition of GLONASS satellite tracks.
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GPS PPP GPS PPP sidereal GPS dPPP GPS dPPP sidereal GPS+GLONASS dPPP 0.001 0.01 Frequency (Hz)
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Confidential manuscript submitted to Geophysical Research Letters
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Averaged PSD (dB) over all seven baselines (Figure S1) on all 31 days (total about 120 solu-
tions) for the east and up components spanning a wide frequency band from 2 to 50000 s. Note that the two panels have different vertical graduations and scales. More descriptions refer to Figure 3 in the main text.
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Confidential manuscript submitted to Geophysical Research Letters
Figure S8.
One-Hz 24-hour displacements for the east, north and up components at the 14 stations in Spain
(cf. Figure S1) on day 122 of 2016 which have been low pass filtered with a cut-off frequency of 1.4 hours. All time series are offset by 2 cm from each other to avoid overlap.
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Confidential manuscript submitted to Geophysical Research Letters
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Averaged PSDs (dB) over all 99 stations on all 31 days (total about 1500–2200 solutions) for the
north, east and up components spanning a frequency band from 2 to 50000 s. Four types of solutions (cf. the legend) are presented of which the sidereally filtered GPS/GLONASS fixed solutions are shown twice in the insets and the main panels. This figure is almost a duplicate of Figure 2 except for the additional PSDs for the sidereally filtered GPS/GLONASS fixed solutions and the excluded PSDs for float solutions.
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